In this specification, the term “circular substrate” refers to a substrate having a diameter of 2.5 inches, 1.8 inches, 1.0 inches, or 0.85 inches, for example. Of these sizes, substrates with a 2.5-inch diameter have an outer diameter of 65 mm, an inner circular hole diameter of 20 mm, and a thickness of 0.635 mm; substrates with a 1.8-inch diameter have an outer diameter of 48 mm, an inner circular hole diameter of 12 mm, and a thickness of 0.508 mm; substrates with a 1.0-inch diameter have an outer diameter of 27.4 mm, an inner circular hole diameter of 7 mm, and a thickness of 0.381 mm; and substrates with a 0.85-inch diameter have an outer diameter of 21.6 mm, an inner circular hole diameter of 6 mm, and a thickness of 0.381 mm.
A conventional method for polishing the inner peripheral edge surface of the circular hole formed in this type of circular substrate involves rotating a polishing brush or a polishing pad in contact with the inner peripheral edge surface while supplying an abrasive liquid containing free abrasive grains thereto.